Polycrystalline CoO−Co9S8 Heterostructure Nanoneedle Arrays as Bifunctional Catalysts for Efficient Overall Water Splitting

Graphical One-dimensional nanoneedles : An efficient catalyst for overall water splitting is prepared by modulating the electron density of Co 2+ /Co 3+ via the formation of a CoO−Co 9 S 8 heterostructure. It is a great challenge to synthesize efficient electrocatalysts for overall water splitting, especially non-noble metal catalysts. Herein, one-dimensional polycrystalline nanoneedles composed of CoO−Co 9 S 8 nano heterostructures, in situ grown on carbon fiber paper are prepared for efficient overall water electrolysis. Due to strong electronic coupling, charge densities of Co 2+ /Co 3+ in Co 9 S 8 and Co 2+ in CoO are favorably modified at the interface of CoO and Co 9 S 8 , resulting in optimized reaction intermediates absorption and greatly enhanced bifunctional HER/OER activities. CoO−Co 9 S 8 /CFP delivers a current density of 10 mA cm −2 in alkaline electrolyte at overpotentials of 184 mV and 270 mV for HER and OER, respectively. When used as electrocatalyst for overall water splitting, it needs a low cell potential of 1.66 V to realize water electrolysis at 10 mA cm −2 . This work provides a new strategy to tune the electronic structures of transitional metal active sites via constructing nano heterostructures for efficient water electrolysis.